1. Field of the Invention
The present invention relates to an optical disc and a recording method, and more specifically to an optical disc of the writable type with pregrooves and a recording method and apparatus using an optical disc of that type.
2. Description of Background Information
A recording method has already been developed by which an FM modulated video format signal is recorded on an optical disc with pregrooves, so as to enable the recording and reproduction of pictures with motion. In such a conventional recording method, a vertical sync signal is recorded on the disc beforehand. During the recording of the video format signal the vertical sync signal is read-out from the disc, so that the rotational speed of the disc is controlled in response to the phase difference between the vertical sync signal obtained from the disc and the vertical sync signal in the video format signal to be recorded.
However, since the vertical sync signal is recorded every half a revolution of the disc, there has been the problem that the eccentricity of the disc and the fluctuation of the rotation of the spindle motor cause errors of in the linear velocity, so that the time error becomes large at the boundary between fields or frames of the video format signal. This time error generated at the boundary between fields or frames becomes as large as 0.16H (1H is 64.mu.s) when the eccentricity is 50 .mu.m, the rotational speed is 1800 rpm, and the distance between the center of rotation and the position of irradiation of the light beam for writing information is 55 millimeter.
Therefore, apparatuses for reproducing information recorded on the disc on which the video format signal is recorded by the above described conventional recording system have needed a complex device for preventing disturbances of image caused by a malfunction of a circuit for compensating the time base error or the like, such as a device disclosed in a research paper titled "Efficient Synchronization of Play Back Video with External Video Sync in Recordable Optical Disc," printed in the digest of technical papers of Optical Memory Symposium '86, pp 197-200.